Synthesis and investigation of poly(p-phenylenediamine)–poly(1,4-benzoquinonediimine-N,N-diyl-1,4-phenylene)

Functionalization of Conductive Polymers through Covalent Postmodification

Organic chemical reactions have been used to functionalize preformed conducting polymers (CPs). The extensive work performed on polyaniline (PANI), polypyrrole (PPy), and polythiophene (PT) is described together with the more limited work on other CPs. Two approaches have been taken for the functionalization: (i) direct reactions on the CP chains and (ii) reaction with substituted CPs bearing reactive groups (e.g., ester). Electrophilic aromatic substitution, S_EAr, is directly made on the non-conductive (reduced form) of the CPs. In PANI and PPy, the N-H can be electrophilically substituted. The nitrogen nucleophile could produce nucleophilic substitutions (SN) on alkyl or acyl groups. Another direct reaction is the nucleophilic conjugate addition on the oxidized form of the polymer (PANI, PPy or PT). In the case of PT, the main functionalization method was indirect, and the linking of functional groups via attachment to reactive groups was already present in the monomer. The same is the case for most other conducting polymers, such as poly(fluorene). The target properties which are improved by the functionalization of the different polymers is also discussed.

Chemical Oxidative Condensation of Benzidine in Non-Aqueous Medium: Synthesis and Investigation of Oligomers and Polymer with Benzidine Diimine Units

The oxidative condensation of benzidine has been carried out in acetic acid media using potassium peroxydisulfate as the oxidizing agent. Using different monomer–oxidant molar ratios, benzidine dimer, trimer, and polymer have been synthesized for the first time. It was established that the polybenzidine structure is composed from a sequence of benzidinediimine and diphenylene units with amino/amino end groups and thus proves the possibility of ammonia elimination during the oxidative polymerization of aromatic diamines. The method seems to be common for the synthesis of polymers with the sequence of aromatic diimine and arylene units. TGA analysis of the obtained trimer and polymer was investigated, and the high thermostability of both the polymer and trimer was revealed. According to the obtained data, both polymer and trimer matrix decomposition started at 300 °C, and at 600 °C, 75.94% and of 69.40% of the initial weight remained, correspondingly. Conductivities of the polymer and trimer show a semiconductor-type change from temperature and after doping show an increase in conductivity up to 10⁻⁴ Sm/cm.

Reversible Oxygen Sensing Based on Multi-Emission Fluorescence Quenching

Oxygen is ubiquitous in nature and it plays a key role in several biological processes, such as cellular respiration and food deterioration, to name a few. Currently, reversible and non-destructive oxygen sensing is usually performed with sensors produced by photosensitization of phosphorescent organometallic complexes. In contrast, we propose a novel route of optical oxygen sensing by fluorescence-based quenching of oxygen. We hereby developed for the first time a set of multi-emissive purely organic emitters. These were produced through a one-pot hydrothermal synthesis using p-phenylenediamine (PPD) and urea as starting materials. The origin of the multi-emission has been ascribed to the diversity of chemical structures produced as a result of oxidative oligomerization of PPD. A Bandrowski's base (BB, i.e., trimer of PPD) is reported as the main component at reaction times higher than 8 h. This indication was confirmed by electrospray-ionization quadrupole time-of-flight (ESI-QTOF) and liquid chromatography-mass spectrometry (LC-MS) analysis. Once the emitters are embedded within a high molecular weight poly (vinyl alcohol) matrix, the intensities of all three emission centers exhibit a non-linear quenching provoked by oxygen within the range of 0-8 kPa. The detection limit of the emission centers are 0.89 kPa, 0.67 kPa and 0.75 kPa, respectively. This oxygen-dependent change in fluorescence emission is reversible (up to three tested 0-21% O₂ cycles) and reproducible with negligible cross-interference to humidity. The cost-effectiveness, metal-free formulation, cross-referencing between each single emission center and the relevant oxygen range are all appealing features, making these sensors promising for the detection of oxygen, e.g., in food packaged products.